Combined optical and electrical neural stimulation

ABSTRACT

A neural-stimulating device for stimulating nerve cells of a recipient is provided. The neural-stimulating device comprises an electromagnetic radiation source configured to generate one or more optical stimulation signals and an electrical stimulation generator configured to generate electrical stimulation signals. The neural-stimulating device also comprises an implantable stimulating assembly configured to be implanted in the recipient, and having disposed thereon an optical contact to deliver the one or more optical stimulation signals to the nerve cells, and an electrical contact to deliver the electric stimulation signals to the nerve cells.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 12/348,225 filed Jan. 2, 2009, which is a related to commonly ownedand co-pending U.S. patent application entitled “A NEURAL-STIMULATINGDEVICE FOR GENERATING PSEUDOSPONTANEOUS NEURAL ACTIVITY,” and commonlyowned and co-pending U.S. patent application entitled “AN OPTICAL NEURALSTIMULATING DEVICE HAVING A SHORT STIMULATING ASSEMBLY,” both filedconcurrently herewith. Both of these applications are herebyincorporated by reference herein in their entirety.

BACKGROUND

1. Field of the Invention

The present invention relates generally to stimulating medical devicesand, more particularly, to combined optical and electrical neuralstimulation.

2. Related Art

Hearing loss, which may be due to many different causes, is generally oftwo types, conductive and sensorineural. In some cases, a person mayhave hearing loss of both types. Conductive hearing loss occurs when thenormal mechanical pathways for sound to reach the hair cells in thecochlea are impeded, for example, by damage to the ossicles. Conductivehearing loss is often addressed with conventional hearing aids whichamplify sound so that acoustic information can reach the cochlea.

In many people who are profoundly deaf, however, the reason for theirdeafness is sensorineural hearing loss. Sensorineural hearing lossoccurs when there is damage to the inner ear or to the nerve pathwaysfrom the inner ear to the brain. Those suffering from sensorineuralhearing loss are thus unable to derive suitable benefit fromconventional hearing aids. As a result, specific neural-stimulatingdevices, referred to herein as electrically-stimulating auditoryprostheses, have been developed to provide persons having sensorineuralhearing loss with the ability to perceive sound. Suchelectrically-stimulating auditory prostheses deliver electricalstimulation to nerve cells of the recipient's auditory system.

As used herein, the recipient's auditory system includes all sensorysystem components used to perceive a sound signal, such as hearingsensation receptors, neural pathways, including the auditory nerve andspiral ganglion, and parts of the brain used to sense sounds.Electrically-stimulating auditory prostheses include, for example,auditory brain stimulators and cochlear™ prostheses (commonly referredto as cochlear™ prosthetic devices, cochlear™ implants, cochlear™devices, and the like; simply “cochlear implants” herein.)

Most sensorineural hearing loss is due to the absence or destruction ofthe cochlear hair cells which transduce acoustic signals into nerveimpulses. It is for this purpose that cochlear implants have beendeveloped. Cochlear implants use direct electrical stimulation ofauditory nerve cells to bypass absent or defective hair cells thatnormally transduce acoustic vibrations into neural activity. Suchdevices generally use an electrode array implanted into the scalatympani of the cochlea so that the electrodes may differentiallyactivate auditory neurons that normally encode differential pitches ofsound.

Auditory brain stimulators are used to treat a smaller number ofrecipients with, for example, bilateral degeneration of the auditorynerve. For such recipients, the auditory brain stimulator providesstimulation of the cochlear nucleus in the brainstem.

SUMMARY

In one aspect of the present invention a neural-stimulating device forstimulating nerve cells of a recipient is provided. The devicecomprises: an electromagnetic radiation source configured to generateone or more optical stimulation signals; an electrical stimulationgenerator configured to generate one or more electrical stimulationsignals; and an implantable stimulating assembly configured to beimplanted in the recipient and having disposed thereon an opticalcontact to deliver the one or more optical stimulation signals to atleast some of the nerve cells, and an electrical contact configured todeliver the electric stimulation signals to at least some of the nervecells.

In another aspect of the present invention, a method for stimulatingnerve cells of a recipient is provided. The method comprises: generatingone or more optical stimulation signals; delivering the one or moreoptical stimulation signals to the nerve cells; generating one or moreelectrical stimulation signals; and delivering the one or moreelectrical stimulation signals to the nerve cells.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are described below with referenceto the attached drawings, in which:

FIG. 1 is a perspective view of an implanted cochlear implant which maybe advantageously configured to implement embodiments of the presentinvention;

FIG. 2A is a perspective, partially cut-away view of a cochlea exposingthe canals and nerve fibers of the cochlea;

FIG. 2B is a cross-sectional view of one turn of the canals of a humancochlea;

FIG. 3 is a side view of the implantable component of a cochlear implantin accordance with embodiments of the present invention;

FIG. 4 is a detailed functional block diagram illustrating thecomponents of a cochlear implant in accordance with embodiments of thepresent invention;

FIG. 5A is a side view of a distal region of a stimulating assemblyschematically illustrating the spread of optical and electricalstimulation in accordance with embodiments of the present invention;

FIG. 5B is a side view of a distal region of a stimulating assemblyschematically illustrating the spread of optical and electricalstimulation in accordance with embodiments of the present invention;

FIG. 5C is a graph illustrating the spread of electrical stimulationalong a recipient's cochlea;

FIG. 6A is a side view of a distal region of a stimulating assemblyschematically illustrating the spread of optical and electricalstimulation in accordance with embodiments of the present invention;

FIG. 6B is a side view of a distal region of a stimulating assemblyschematically illustrating the spread of optical and electricalstimulation in accordance with embodiments of the present invention;

FIG. 7 is graph illustrating the various phases of an idealized actionpotential as the potential passes through a nerve cell, illustrated inmembrane voltage versus time;

FIG. 8 diagram illustrating the membrane voltage versus time of arecipient's nerve cells along with the resulting nerve activity;

FIG. 9 is a diagram illustrating exemplary optical and electricalstimulation signals used to stimulate a recipient's nerve cells inaccordance with embodiments of the present invention;

FIG. 10A is a high level flowchart illustrating operations that may beperformed to encourage, facilitate or allow pseudospontaneous nerveactivity to occur using optical stimulation in accordance withembodiments of the present invention;

FIG. 10B is a detail level flowchart illustrating operations that may beperformed in a cochlear implant in accordance with certain embodimentsof the present invention;

FIG. 11A is a diagram illustrating exemplary optical and electricalstimulation signals used to stimulate a recipient's nerve cells inaccordance with embodiments of the present invention;

FIG. 11B is a diagram illustrating exemplary optical and electricalstimulation signals used to stimulate a recipient's nerve cells inaccordance with embodiments of the present invention;

FIG. 12 is a flowchart illustrating the operations performed in acochlear implant in accordance with embodiments of the presentinvention;

FIGS. 13A is a diagram illustrating exemplary optical and electricalstimulation signals used to stimulate a recipient's nerve cells inaccordance with embodiments of the present invention;

FIG. 13B is a diagram illustrating exemplary optical and electricalstimulation signals used to stimulate a recipient's nerve cells inaccordance with embodiments of the present invention;

FIG. 13C is a diagram illustrating exemplary optical and electricalstimulation signals used to stimulate a recipient's nerve cells inaccordance with embodiments of the present invention;

FIG. 14 is a flowchart illustrating the operations performed in acochlear implant in accordance with embodiments of the presentinvention;

FIG. 15 is a diagram illustrating the membrane voltage versus time of aregion of a recipient's nerve prior to and during the application ofoptical stimulation thereto, as well as an exemplary optical stimulationsignal which may result in the illustrated membrane voltage, inaccordance with embodiments of the present invention;

FIG. 16 is a diagram illustrating exemplary optical and electricalstimulation signals used to stimulate a recipient's nerve cells inaccordance with embodiments of the present invention;

FIG. 17 is a flowchart illustrating the operations performed in acochlear implant in accordance with embodiments of the presentinvention;

FIG. 18A is a side view of an implantable stimulating assembly inaccordance with embodiments of the present invention;

FIG. 18B is a side view of an implantable stimulating assembly inaccordance with embodiments of the present invention;

FIG. 18C is a side view of an implantable stimulating assembly inaccordance with embodiments of the present invention;

FIG. 18D is a side view of an implantable stimulating assembly inaccordance with embodiments of the present invention;

FIG. 18E is a side view of an implantable stimulating assembly inaccordance with embodiments of the present invention;

FIG. 19 is a simplified side view of cochlea having a short stimulatingassembly in accordance with embodiments of the present inventionimplanted therein;

FIG. 20 is a top-view of a distal region of a short stimulating assemblyin accordance with embodiments of the present invention;

FIG. 21 is a schematic diagram illustrating a region of a stimulatingassembly in accordance with embodiments of the present invention;

FIG. 22 is a simplified schematic diagram illustrating an implantablecomponent of a cochlea implant in accordance with embodiments of thepresent invention;

FIG. 23 is cross-sectional view of an optical fiber which may beadvantageously used in embodiments of the present invention;

FIG. 24A is a schematic view of a distal region of an optical fiberwhich may be advantageously used in embodiments of the presentinvention;

FIG. 24B is a schematic view of a distal region of an optical fiberwhich may be advantageously used in embodiments of the presentinvention;

FIG. 25 is a cross-sectional view of a micro-laser that may be used inembodiments of the present invention.

FIG. 26 is a cross-sectional view of a region of a stimulating assemblyillustrating the direction of travel of light in accordance with certainembodiments of the present invention;

FIG. 27A is an enlarged cross-sectional view of a converging lens thatmay be used in an optical contact in accordance with embodiments of thepresent invention; and

FIG. 27B is an enlarged cross-sectional view of a diverging lens thatmay be used in an optical contact in accordance with embodiments of thepresent invention.

DETAILED DESCRIPTION

Aspects of the present invention are generally directed to aneural-stimulating device configured to deliver combinations of opticaland electrical stimulation signals to a recipient's nerve cells.Specifically, embodiments of the present invention are generallydirected to a neural-stimulating device comprising an electromagneticradiation (EMR) generator that generates optical stimulation signals andan electrical stimulation generator to generate electrical stimulationsignals. The neural-stimulating device further comprises an implantablestimulating assembly having optical contacts and electrical contacts.Optical stimulation signals are applied to the recipient's nerve cellsvia optical contacts, while electrical stimulation signals are appliedto the recipient's nerve cells via electrical contacts.

As used herein, optical stimulation signals consist of pulses ofelectromagnetic radiation. The electromagnetic radiation is not limitedto the portion of the electromagnetic spectrum that is visible to thehuman eye, commonly referred to as the optical or visible spectrum.Rather, the electromagnetic radiation may comprise other portions of theelectromagnetic spectrum such as the ultraviolet, visible, infrared, farinfrared or deep infrared radiation.

Embodiments of the present invention are described herein primarily inconnection with one type of neural-stimulating device, namelyelectrically-stimulating auditory prostheses. Electrically-stimulatingauditory prostheses deliver electrical stimulation to one or more nervecells of the recipient's auditory system. As used herein, therecipient's auditory system includes all sensory system components usedto perceive a sound signal, such as hearing sensation receptors, neuralpathways, including the auditory nerve and spiral ganglion, and parts ofthe brain used to sense sounds. As such, electrically-stimulatingauditory prostheses include, for example, auditory brain stimulators andcochlear implants.

As noted, cochlear implants stimulate auditory nerve cells, bypassingabsent or defective hair cells that normally transduce acousticvibrations into neural activity. Cochlear implants generally use anarray of electrodes inserted into or adjacent the cochlea so that theelectrodes may activate auditory neurons that normally encodedifferential pitches of sound. Auditory brain stimulators are used totreat a smaller number of recipients, such as those with bilateraldegeneration of the auditory nerve. The auditory brain stimulatorcomprises an array of electrodes configured to be positioned, forexample, proximal to the recipient's brainstem. When implanted, theelectrodes apply electrical stimulation signals to the cochlear nucleusin the brainstem, resulting in a hearing sensation by the recipient.Although embodiments of the present invention are described herein withreference to such electrically-stimulating auditory prostheses, itshould be appreciated that embodiments of the present invention,regardless of whether described herein, may be implemented in anyneural-stimulating device now known or later developed.

FIG. 1 is perspective view of an electrically-stimulating auditoryprosthesis, namely a cochlear implant. An exemplary cochlear implant 100is shown implanted in a recipient, in which embodiments of the presentinvention may be implemented. The relevant components of outer ear 101,middle ear 105 and inner ear 107 are described next below, followed by adescription of cochlear implant 100.

In a fully functional ear, outer ear 101 comprises an auricle 110 and anear canal 102. An acoustic pressure or sound wave 103 is collected byauricle 110 and channeled into and through ear canal 102. Disposedacross the distal end of ear cannel 102 is a tympanic membrane 104 whichvibrates in response to sound wave 103. This vibration is coupled tooval window or fenestra ovalis 112 through three bones of middle ear105, collectively referred to as the ossicles 106 and comprising themalleus 108, the incus 109 and the stapes 111. Bones 108, 109 and 111 ofmiddle ear 105 serve to filter and amplify sound wave 103, causing ovalwindow 112 to articulate, or vibrate in response to vibration oftympanic membrane 104. This vibration sets up waves of fluid motion ofthe perilymph within cochlea 140. Such fluid motion, in turn, activatestiny hair cells (not shown) inside cochlea 140. Activation of the haircells causes appropriate nerve impulses to be generated and transferredthrough the spiral ganglion cells (not shown) and auditory nerve 114 tothe brain (also not shown) where they are perceived as sound.

Cochlear implant 100 comprises an external component 142 which isdirectly or indirectly attached to the body of the recipient, and aninternal component 144 which is temporarily or permanently implanted inthe recipient. External component 142 typically comprises one or moreacoustic pickup devices, such as microphone 124, for detecting sound, asound processing unit 126, a power source (not shown), and an externaltransmitter unit 128. External transmitter unit 128 comprises anexternal coil 130 and, preferably, a magnet (not shown) secured directlyor indirectly to external coil 130. Sound processing unit 126 processesthe output of microphone 124 that is positioned, in the depictedembodiment, adjacent auricle 110 of the recipient. Sound processing unit126 generates encoded signals, sometimes referred to herein as encodeddata signals, which are provided to external transmitter unit 128 via acable (not shown).

Internal component 144 comprises, in this depicted embodiment, aninternal receiver unit 132, a stimulator unit 120, and an elongatestimulating assembly 118. Internal receiver unit 132 comprises aninternal coil 136, and preferably, a magnet (also not shown) fixedrelative to the internal coil. Internal receiver unit 132 and stimulatorunit 120 are hermetically sealed within a biocompatible housing,sometimes collectively referred to as a stimulator/receiver unit. Themagnets facilitate the operational alignment of the external andinternal coils, enabling internal coil 136 to receive power andstimulation data from external coil 130, as noted above. Elongatestimulating assembly 118 has a proximal end connected to stimulator unit120, and a distal end implanted in cochlea 140. Stimulating assembly 118extends from stimulator unit 120 to cochlea 140 through mastoid bone119. Stimulating assembly 118 is implanted into cochlea 104. Asdescribed below, stimulating assembly is implanted in cochlea 140. Insome embodiments, stimulating assembly 118 may be implanted at least inbasal region 116, and sometimes further. For example, stimulatingassembly 118 may extend towards apical end of cochlea 140, referred toas cochlea apex 134. In certain circumstances, stimulating assembly 118may be inserted into cochlea 140 via a cochleostomy 122. In othercircumstances, a cochleostomy may be formed through round window 121,oval window 112, the promontory 123 or through an apical turn 147 ofcochlea 140.

Stimulating assembly 118 comprises a longitudinally aligned and distallyextending array 146 of stimulating contacts 148, sometimes referred toas contact array 146 herein, disposed along a length thereof. Althoughcontact array 146 may be disposed on stimulating assembly 118, in mostpractical applications, contact array 146 is integrated into stimulatingassembly 118. As such, for all embodiments of stimulating assembly 118,contact array 146 is generally referred to herein as being disposed instimulating assembly 118. As described below, stimulator unit 120generates stimulation signals which are applied by contacts 148 tocochlea 140, thereby stimulating auditory nerve 114.

In certain embodiments, external coil 130 transmits electrical signals(i.e., power and stimulation data) to internal coil 136 via a radiofrequency (RF) link, as noted above. Internal coil 136 is typically awire antenna coil comprised of multiple turns of electrically insulatedsingle-strand or multi-strand platinum or gold wire. The electricalinsulation of internal coil 136 is provided by a flexible siliconemolding (not shown). In use, implantable receiver unit 132 may bepositioned in a recess of the temporal bone adjacent auricle 110 of therecipient.

There are several speech coding strategies that may be implemented bysound processing unit 126 to convert sound 103 into the encoded datasignals. Embodiments of the present invention may be used in combinationwith any speech strategy now or later developed, including but notlimited to Continuous Interleaved Sampling (CIS™), Spectral PEAKExtraction (SPEAK™), Advanced Combination Encoders (ACE™), SimultaneousAnalog Stimulation (SAS), MPS, Paired Pulsatile Sampler (PPS), QuadruplePulsatile Sampler (QPS), Hybrid Analog Pulsatile (HAPs), n-of-m andHiRes®, developed by Advanced Bionics. SPEAK™ is a low rate strategythat may operate within the 250-500 Hz range. ACE™ is a combination ofCIS™ and SPEAK™. Examples of such speech strategies are described inU.S. Pat. No. 5,271,397, which is hereby incorporated by referenceherein. The present invention may also be used with other speech codingstrategies, such as a low rate strategy called Spread of Excitationwhich is described in U.S. Provisional No. 60/557,675 entitled, “SpreadExcitation and MP3 coding Number from Compass UE” filed on Mar. 31,2004, U.S. Provisional No. 60/616,216 entitled, “Spread of ExcitationAnd Compressed Audible Speech Coding” filed on Oct. 7, 2004, and PCTApplication WO 02/17679A1, entitled “Power Efficient ElectricalStimulation,” which are hereby incorporated by reference herein. Certainembodiments of the present invention may be used on Cochlear Limited'sNucleus™ implant system that uses a range of coding strategiesalternatives, including SPEAK™, ACE™, and CIS™. (HiRes is a registeredtrademark of Advanced Bionics Corporation, Sylmar, Calif., USA. SPEAK,ACE, and CIS are trademarks of Cochlear Limited, Lane Cove, NSW,Australia).

Embodiments of cochlear implant 100 may locally store several speechstrategies, such as in the form of a software program or otherwise, anyone of which may be selected depending, for example, on the auralenvironment. For example, a recipient may choose one strategy for a lownoise environment, such as a conversation in an enclosed room, and asecond strategy for a high noise environment, such as on a publicstreet. The programmed speech strategies may be different versions ofthe same speech strategy, each programmed with different parameters orsettings.

Relevant aspects of cochlea 140 are described next below with referenceto FIGS. 2A-2C. FIG. 2A is a perspective view of cochlea 140 partiallycut-away to display the canals and nerve fibers of the cochlea. FIG. 2Bis a cross-sectional view of one turn of the canals of cochlea 140. Tofacilitate understanding, the following description will reference thecochlea illustrated in FIGS. 2A and 2B as cochlea 140, which wasintroduced above with reference to FIG. 1.

Referring to FIG. 2A, cochlea 140 is a conical spiral structurecomprising three parallel fluid-filled canals or ducts, collectively andgenerally referred to herein as canals 202. Canals 202 comprise thetympanic canal 208, also referred to as the scala tympani 208, thevestibular canal 204, also referred to as the scala vestibuli 204, andthe median canal 206, also referred to as the scala media 206. Cochlea140 has a conical shaped central axis, the modiolus 212, that forms theinner wall of scala vestibuli 204 and scala tympani 208. Tympanic andvestibular canals 208, 204 transmit pressure, while medial canal 206contains the organ of corti 210 which detects pressure impulses andresponds with electrical impulses which travel along auditory nerve 114to the brain (not shown).

Cochlea 140 spirals about modiolus 212 several times and terminates atcochlea apex 134. Modiolus 212 is largest near its base where itcorresponds to first turn 241 of cochlea 140. The size of modiolus 212decreases in the regions corresponding to medial 242 and apical turns246 of cochlea 140.

Referring now to FIG. 2B, separating canals 202 of cochlear 140 arevarious membranes and other tissue. The Ossicous spiral lamina 222projects from modiolus 212 to separate scala vestibuli 204 from scalatympani 208. Toward lateral side 218 of scala tympani 208, a basilarmembrane 224 separates scala tympani 208 from scala media 206.Similarly, toward lateral side 218 of scala vestibuli 204, a vestibularmembrane 226, also referred to as the Reissner's membrane 226, separatesscala vestibuli 204 from scala media 206.

Portions of cochlea 140 are encased in a bony capsule 216. Bony capsule216 resides on lateral side 218 (the right side as illustrated in FIG.2B), of cochlea 140. Spiral ganglion cells 214 reside on the opposingmedial side 220 (the left side as illustrated in FIG. 2B) of cochlea140. A spiral ligament membrane 230 is located between lateral side 218of spiral tympani 208 and bony capsule 216, and between lateral side 218of scala media 206 and bony capsule 216. Spiral ligament 230 alsotypically extends around at least a portion of lateral side 218 of scalavestibuli 204.

The fluid in tympanic and vestibular canals 208, 204, referred to asperilymph, has different properties than that of the fluid which fillsscala media 206 and which surrounds organ of Corti 210, referred to asendolymph. Sound entering auricle 110 causes pressure changes in cochlea140 to travel through the fluid-filled tympanic and vestibular canals208, 204. As noted, organ of Corti 210 is situated on basilar membrane224 in scala media 206. It contains rows of 16,000-20,000 hair cells(not shown) which protrude from its surface. Above them is the tectoralmembrane 232 which moves in response to pressure variations in thefluid-filled tympanic and vestibular canals 208, 204. Small relativemovements of the layers of membrane 232 are sufficient to cause the haircells in the endolymph to move thereby causing the creation of a voltagepulse or action potential which travels along the associated nerve fiber228. Nerve fibers 228, embedded within spiral lamina 222, connect thehair cells with the spiral ganglion cells 214 which form auditory nerve114. Auditory nerve 114 relays the impulses to the auditory areas of thebrain (not shown) for processing.

The place along basilar membrane 224 where maximum excitation of thehair cells occurs determines the perception of pitch and loudnessaccording to the place theory. Due to this anatomical arrangement,cochlea 140 has characteristically been referred to as being“tonotopically mapped.” That is, regions of cochlea 140 toward basalregion 116 are responsive to high frequency signals, while regions ofcochlea 140 toward apical end 116 are responsive to low frequencysignals. These tonotopical properties of cochlea 140 are exploited in acochlear implant by delivering stimulation signals within apredetermined frequency range to a region of the cochlea that is mostsensitive to that particular frequency range.

FIG. 3 is a simplified side view of an embodiment of internal component144, referred to herein as internal component 344. As shown in FIG. 3,internal component 344 comprises a stimulator/receiver unit 302 which,as described above, receives encoded signals from an external componentof the cochlear implant. Internal component 344 terminates in astimulating assembly 318 that comprises an extra-cochlear region 310 andan intra-cochlear region 312. Intra-cochlear region 312 is configured tobe implanted in the recipient's cochlea and has disposed thereon anarray 316 of contacts. In the illustrative embodiment of FIG. 3, contactarray 316 comprises optical contacts 320 and electrical contacts 330. Asdescribed in greater detail below, contact array 316 may comprise anynumber of optical or electrical contacts 320, 330, in a variety ofarrangements.

In certain embodiments, stimulating assembly 318 is configured to adopta curved configuration during and or after implantation into therecipient's cochlea. To achieve this, in certain embodiments,stimulating assembly 318 is pre-curved to the same general curvature ofa cochlea. Such embodiments of stimulating assembly 318, sometimesreferred to as perimodiolar stimulating assemblies, are typically heldstraight by, for example, a stiffening stylet (not shown) which isremoved during implantation so that the stimulating assembly may adoptits curved configuration when in the cochlea. Other methods ofimplantation, as well as other stimulating assemblies which adopt acurved configuration, may be used in alternative embodiments of thepresent invention.

In other embodiments, stimulating assembly 318 is a non-perimodiolarstimulating assembly which does not adopt a curved configuration. Forexample, stimulating assembly 318 may comprise a straight stimulatingassembly or a mid-scala assembly which assumes a mid-scala positionduring or following implantation.

In certain embodiments, stimulator/receiver unit 302 may include one ormore electromagnetic radiation (EMR) generators (not shown) and mayinclude an electrical stimulation generator (also now shown) whichgenerate optical and electrical stimulation signals, respectively, forapplication to the auditory nerve cells of the cochlear implantrecipient. As described below, in other embodiments, the one or more EMRgenerators may be included in stimulating assembly 318.

Internal component 344 further comprises a lead region 308 couplingstimulator/receiver unit 302 to stimulating assembly 318. Lead region308 comprises a helix region 304 and a transition region 306. Helixregion 304 is a section of lead region 308 in which electrode leads arewould helically. Transition region 306 connects helix region 304 tostimulating assembly 318. As described below, optical and/or electricalstimulation signals generated by stimulator/receiver unit 302 aredelivered to contact array 316 via lead region 308. Helix region 304prevents lead region 308 and its connection to stimulator/receiver 302and stimulating assembly 318 from being damaged due to movement ofinternal component 144 which may occur, for example, during mastication.

FIG. 4 is a detailed functional block diagram illustrating thecomponents of an embodiment of cochlear implant 100, referred to hereinas cochlear implant 400. As shown, elements of cochlear implant 400 thathave substantially the same or similar structures and/or performssubstantially the same or similar functions as elements of cochlearimplant 100 are illustrated in FIG. 4 using a 400 series referencenumber having two right digits which are the same as the right twodigits as the corresponding element of FIG. 1. For example, as shown,cochlear implant 400 comprises an embodiment of external component 142of FIG. 1, referred to as external component 442.

In the illustrative embodiment of FIG. 4, external component 442comprises a behind-the-ear (BTE) device 434 and one or more sound inputelements, such as microphone 424. BTE 434 is configured to be wornbehind the ear of the recipient and, as described herein, may comprisevarious sound processing and other components. Microphone 424 may bepositionable on BTE 434 or elsewhere on the recipient, and is configuredto receive acoustic sound signals.

As would be appreciated by those of ordinary skill in the art, althoughthe embodiments of FIG. 4 are described with reference to externalcomponent 442 configured as a BTE, other configurations of externalcomponent 442 may also be implemented in embodiments of the presentinvention. For example, in certain embodiments, external component 442may be configured as a body-worn sound processing unit instead of, or incombination with, a component that is worn behind the ear. In otherembodiments, external component 442 may be omitted and microphone 424 aswell as the components residing in BTE device 434 may be implanted inthe recipient. Such an arrangement of a cochlear implant is sometimesreferred to as a totally-implantable cochlear implant. For ease ofdescription, embodiments of the present invention will be primarilydescribed herein with reference to cochlear implants having externalcomponents. However, embodiments of the present invention may be equallyimplemented in any cochlear implant now known or later developed.

As shown in FIG. 4, BTE device 434 comprises a sound processing unit450, a transmitter 452 and a control module 454. As noted above,microphone 424 receives acoustic sound signals and deliverscorresponding electrical signals to a preprocessor 432 of soundprocessing unit 450. Preprocessor 432 filters the electrical signals anddelivers certain signals to an optical signal module 446 and certainsignals to an electrical signal module 448. The filtering bypreprocessor 432 may be based on a variety of factors including thefrequency of the received signals, the current mode of operation ofcochlear implant 400, or other criteria, at least some of which arespecified to preprocessor 432 via control signals generated by controlmodule 454. Optical signal module 446 performs signal processingoperations on electrical signals received from preprocessor 432 into oneor more encoded data signals 472 which are delivered to internalcomponent 444 by transmitter 452. Electrical signal module 448 performssignal processing operations on the received signals to convert theelectrical signals received from preprocessor 432 into one or moreencoded data signals 474 which are also transmitted to internalcomponent 444 by transmitter 452.

External component 442 may further comprise a control module 454.Control module 454 may be configured to receive control inputs from arecipient, an external device, or internally generated events, commandsor interrupts. Control module 454 controls sound processing unit 450and/or transmission of signals to internal component 444. As describedbelow, in one embodiment, control module causes a control signal 475 tobe transmitted to internal component 444.

In the embodiments illustrated in FIG. 4, cochlear implant 400 alsoincludes an internal component 444 comprising a stimulator/receiver unit402 and a stimulating assembly 418. Stimulator/receiver unit 402comprises a receiver module 458 that receives from transmitter 452encoded data signals 472, 474 and, in this illustrative embodiment,control signals 475. As shown, stimulator/receiver unit 402 includes anelectromagnetic radiation (EMR) generator 462 that generates opticalstimulation signals 463. Optical stimulation signals 463 are deliveredto the recipient via optical contacts 420 of stimulating assembly 418.In certain embodiments, EMR generator 462 generates optical stimulationsignals 463 based on encoded data signals 472. In other embodiments, EMRgenerator 462 generates optical stimulation signals 463 additionally oralternatively based on control signals 475. The application of opticalstimulation signals 463 is described in greater detail below.

As shown, stimulator/receiver 402 also includes an electricalstimulation generator 460 that generates electrical stimulation signals465 which are applied to the recipient via electrical contacts 430 ofstimulating assembly 418. In some embodiments, electrical stimulationgenerator 460 generates electrical stimulation signals 465 based onencoded data signals 474. In other embodiments, electrical stimulatorgenerator 460 generates electrical stimulation signals 465 additionallyor alternatively based on one or more control signals 475 from controlmodule 454. Stimulator/receiver unit 402 may generate opticalstimulation signals 463 simultaneously or sequentially with electricalstimulation signals 465.

As noted, optical contacts 420 and electrical contacts 430 applyrespective optical and electrical stimulation signals to the recipient.FIGS. 5A-5B and FIGS. 6A-6B are simplified side views of a distalportion of an elongate stimulating assembly 518 with combinations ofoptical and electrical contacts 520, 530 in accordance with embodimentsof the present invention. The emission of energy is depicted with arrows522, 524 and 532 in FIGS. 5A and 5B, and by arrows 622, 624 and 632 inFIGS. 6A and 6B. It should be appreciated that interpretation of thefigures representing a given moment in time reflect embodiments of acochlear implant that provide simultaneous stimulation; that is theemissions 522, 532 are emitted at the same time. Alternatively,interpretation of the figures representing no one moment in timereflects embodiments of a cochlear implant that provide sequentialstimulation; that is, emissions 522 occurs prior to, or subsequent to,emission 532.

For ease of illustration, electrical contacts 530, 630, and opticalcontacts 520, 620, illustrated in FIGS. 5A-6B are shown in exemplarystimulating assemblies in an alternating arrangement. However, asdescribed in greater detail below with reference to FIGS. 18A-18E, otherarrangements may also be implemented.

As is well known to those of ordinary skill in the art, electricalstimulation signals travel though a biological medium in the directionin which the stimulation signals are emitted as well as in directionslateral to the intended direction of travel. This latter phenomenon iscommonly referred to as the spread of excitation. For example, in thecochlea, applied electrical stimulation signals typically travel throughthe perilymph of the cochlea. This electrical stimulation signalstimulates the targeted nerve cells which are longitudinally alignedwith and thus adjacent or proximate the emitting contact, while thespread of the electrical stimulation signal results in the stimulationof nerve cells which are positioned at various longitudinal distancesfrom the emitting contact. This latter stimulation is referred to hereinas dispersed electrical stimulation. The spread of an applied electricalstimulation signal may be affected by a variety of factors such as theintensity of the applied signal and the impedance of the medium throughwhich the electrical stimulation signal propagates. For example,electrical stimulation signals may travel down a cochlea duct due to thelow impedance of the cochlea perilymph. In contrast, the impedance ofthe nerve cells, other cochlea structures, as well as the surroundingbone and cartilage have a relatively higher impedance.

The spread of electrical stimulation signals may also be affected by theapplication of other electrical stimulation signals. For example, recentdevelopments in electrical stimulation technology provide stimulatingmedical devices with the ability to provide electrical stimulation ofonly a spatially narrow or small region of nerve cells immediatelyadjacent or proximate the applying contact. This resulting pattern ofstimulation is referred to herein as focused electrical stimulation.Some exemplary medical devices cause focused electrical stimulationthrough the interaction between two or more electrical stimulationsignals. This interaction is described in commonly-owned and co-pendingU.S. patent application Ser. No. 11/414,360, entitled “FocusedStimulation in a Medical Stimulation Device” and U.S. patent applicationSer. No. 12/172,821, entitled “Use Of Focused Stimuli To Measure ANeural Excitation Profile Within The Cochlea,” both of which are herebyincorporated by reference herein.

Optical stimulation signals generally travel in a relatively direct lineand, as such, generally spread through a biological medium to a lesserextent than electrical stimulation signals. When applied, opticalstimulation signals may cause stimulation of nerve cells adjacent orproximate the emitting contact, as well as nerve cells further along thedirection of travel, such as nerve cells in an adjacent turn of thecochlea. Thus, in embodiments of the present invention, the spread ofexcitation caused by optical stimulation signals may be managed by theconfiguration of the optical contact. As such, in certain embodiments,the optical stimulation signals are applied in a manner which stimulatesonly a spatially narrow or small longitudinal region of nerve cellsadjacent or proximate to the emitting optical contact. This resultingpattern of stimulation is referred to herein as focused opticalstimulation. In other embodiments, optical stimulation signals areapplied to stimulate nerve cells positioned at relatively greaterlongitudinal distances from the emitting optical contact. This resultingpattern of stimulation is referred to herein as dispersed opticalstimulation.

As would be appreciated by one or ordinary skill in the art, the spreadof an applied optical stimulation signal may also be affected by theintensity of the stimulation, the degree to which the opticalstimulation signal is dispersed or focused, and the medium through whichthe optical stimulation signal propagates. For example, in accordancewith certain embodiments of the present invention, the configuration ofoptical contacts 520 may determine the direction of travel of an opticalstimulation signal and/or the spread of the signal from the contact. Theconfiguration of the optical stimulation contacts is described infurther detail below.

Referring to FIG. 5A, a distal portion 516 of an embodiment ofstimulating assembly 118, referred to herein as stimulating assembly 518is shown. Distal portion 516 comprises a plurality of longitudinallyarranged electrical contacts 530 and optical contacts 520. As shown,contacts 520 and 530 are spaced from one another along the length ofstimulating assembly 518. For ease of illustration, electrical contacts530 are depicted as rectangles and optical contacts 520 are depicted asovals. These exemplary shapes are provided only to facilitateunderstanding of embodiments of the present invention and do not defineor limit electrical contacts 530 or optical contacts 520 in any manner.

In the embodiment of FIG. 5A, optical contact 520 is configured and/ororiented such that applied optical stimulation signals 522 aredispersed, resulting in dispersed optical stimulation 509 of cochleatissue 531. Furthermore, in the illustrative embodiments of FIG. 5A,electrical contact 530 is configured and/or oriented such that appliedelectrical stimulation signals 532 are dispersed, resulting in dispersedelectrical stimulation 507 of cochlea tissue 531.

In the embodiments illustrated in FIG. 5B, optical contact 520 isconfigured and/or oriented such that applied optical stimulation signals524 are substantially focused, resulting in focused optical stimulation511 of cochlea tissue 531. Furthermore, in the illustrative embodimentsof FIG. 5B, electrical contact 530 is configured and/or oriented suchthat applied electrical stimulation signals 532 are dispersed, resultingin dispersed electrical stimulation 507 of cochlea tissue 531.

As noted, in certain embodiments of the present invention electricalstimulation signals delivered to a recipient's cochlea will result indispersed stimulation of the cochlea (i.e. stimulation of nerve cellsadjacent or proximate the electrical contact, as well as nerve cellspositioned at various distances from the contact). FIG. 5C is a graphillustrating two exemplary dispersed stimulation patterns resulting fromthe delivery of electrical stimulation signals to a recipient's cochlea.As discussed in greater detail below with reference to FIG. 7, deliveryof electrical stimulation signals to a recipient's cochlea causes nervecells along the cochlea to fire, thereby generating an action potentialwhich is transmitted along the auditory pathway. As such, the graph inFIG. 5C illustrates dispersed stimulation patterns in terms of thenumber of nerve cells which are fired, illustrated as axis 574, atvarious distances along the cochlea from a point of stimulation. Asshown, the point of stimulation is the region of the cochlea where thegreatest number of nerve cells are fired, and the distance along thecochlea is shown as axis 576.

FIG. 5C illustrates a first spread pattern 572 resulting from thedelivery of an electrical stimulation signal at the recipient'sthreshold level (T-Level). In the illustrative embodiment, therecipient's T-Level is 0.4 mA, and the electrical stimulation signal isapplied for 25 microseconds. Therefore, when 0.4 mA of current isapplied for 25 microseconds, the spread of electrical stimulation isillustrated by pattern 572. As shown, the number of nerve cells fireddecreases as the distance from the point of stimulation increases.

FIG. 5C also illustrates a second spread pattern 570 resulting from thedelivery of an electrical stimulation signal at the recipient's comfortlevel (C-Level). In the illustrative embodiment, the recipient's C-Levelis twice the recipient's T-Level, or 0.8 mA, and the electricalstimulation signal is again applied for 25 microseconds. Therefore, when0.8 mA of current is applied for 25 microseconds, the spread ofelectrical stimulation is illustrated by pattern 570. As shown, thenumber of nerve cells fired decreases as the distance from the point ofstimulation increases.

In FIG. 5C, pattern 570 has an approximate width of 10 mm. As such,nerve cells approximately 5 mm on either side of the point ofstimulation are fired. It would be appreciated by one of ordinary skillin the art that the T-Level, C-Level, current levels and times aremerely illustrative, and should not be construed to limit embodiments ofthe present invention.

FIG. 6A illustrates a distal portion 616 of an embodiment of stimulatingassembly 618, referred to herein as stimulating assembly 618. Similar tostimulating assembly 518 described above with reference to FIGS. 5A and5B, stimulating assembly 618 comprises a plurality of longitudinallyarranged electrical contacts 630 and optical contacts 620.

In the embodiment of FIG. 6A, optical contact 620 is configured and/ororiented such that applied optical stimulation signals 622 aredispersed, resulting in dispersed optical stimulation 609 of cochleatissue 631. Furthermore, in the illustrative embodiments of FIG. 6A,electrical contact 630 is configured and/or oriented such that appliedelectrical stimulation signals 632 are substantially focused, resultingin focused electrical stimulation 607 of cochlea tissue 631.

In the embodiments illustrated in FIG. 6B, optical contact 620 isconfigured and/or oriented such that applied optical stimulation signals624 are substantially focused, resulting in focused optical stimulation611 of cochlea tissue 631. Furthermore, in the illustrative embodimentsof FIG. 6B, electrical contact 630 is configured and/or oriented suchthat applied electrical stimulation signals 632 are substantiallyfocused, resulting in focused electrical stimulation 607 of cochleatissue 631.

The embodiments described with reference to FIGS. 5A-6B above have beenprovided for illustrative purposes only. It would be appreciated thatthe various embodiments described above may be combined or otherwisealtered to fit the needs of the recipient or the cochlear implant. Forexample, in certain embodiments of FIGS. 6A, an optical stimulationsignal 622 applied via a first optical contact 620A may cause dispersedoptical stimulation, while an optical stimulation signal (not shown)delivered to a second optical contact 620B may cause focused opticalstimulation. Similarly, in other embodiments of FIG. 6A, an electricalstimulation signal 632 applied via a first electrical contact 630A maycause focused electrical stimulation, while an electrical stimulationsignal delivered to a second electrical contact 630B may cause dispersedelectrical stimulation. As would be appreciated, all variouscombinations of optical and electrical stimulation are within the scopeof the present invention.

As is well known in the art, the human auditory system is composed ofmany structural components, some of which are connected extensively bybundles of nerve cells (neurons). Each nerve cell has a cell membranewhich acts as a barrier to prevent intercellular fluid from mixing withextracellular fluid. The intercellular and extracellular fluids havedifferent concentrations of ions, which leads to a difference in chargebetween the fluids. This difference in charge across the cell membraneis referred to herein as the membrane potential (Vm) of the nerve cell.Nerve cells use membrane potentials to transmit signals betweendifferent parts of the auditory system.

In nerve cells that are at rest (i.e., not transmitting a nerve signal)the membrane potential is referred to as the resting potential of thenerve cell. Upon receipt of a stimulus, the electrical properties of anerve cell membrane are subjected to abrupt changes, referred to hereinas a nerve action potential, or simply action potential. The actionpotential represents the transient depolarization and repolarization ofthe nerve cell membrane. The action potential causes electrical signaltransmission along the conductive core (axon) of a nerve cell. Signalsmay be then transmitted along a group of nerve cells via suchpropagating action potentials.

FIG. 7 is graph illustrating the various phases of an idealized actionpotential 702 as the potential passes through a nerve cell in accordancewith embodiments of the present invention. The action potential ispresented as membrane voltage in millivolts (mV) versus time. As wouldbe appreciated by one of ordinary skill in the art, the membranevoltages and times shown in FIG. 7 are provided for illustrationpurposes only. The actually voltages may vary depending on theindividual. As such, this illustrative example should not be construedas limiting the present invention.

In the example of FIG. 7, prior to application of a stimulus 718 to thenerve cell, the resting potential of the nerve cell is approximately −70mV. Stimulus 718 is applied at a first time. In normal hearing, thisstimulus is provided by movement of the hair cells of the cochlea.Movement of these hair cells results in the release of a nerve impulse,sometimes referred to as neurotransmitter. In embodiments of the presentinvention, the stimulus is the result of the application of opticaland/or electrical stimulation signals to the nerve cells.

As shown in FIG. 7, following application of stimulus 718, the nervecell begins to depolarize. Depolarization of the nerve cell refers tothe fact that the voltage of the cell becomes more positive followingstimulus 718. When the membrane of the nerve cell becomes depolarizedbeyond the cell's critical threshold, the nerve cell undergoes an actionpotential. This action potential is sometimes referred to as the“firing” of the nerve cell. As used herein, the critical threshold of anerve cell, group of nerve cells, etc. refers to the threshold level atwhich the nerve cell, group of nerve cells, etc. will undergo an actionpotential. In the example illustrated in FIG. 7, the critical thresholdlevel for firing of the nerve cell is approximately −50 mV. As would beappreciated, the critical threshold and other transitions may bedifferent for various recipients. As such, the values provided in FIG. 7are merely illustrative. For consistency, a critical threshold of −50 mVwill be used herein, but such usage should not be considered to limitthe present invention

The course of this action potential in the nerve cell can be generallydivided into five phases. These five phases are shown in FIG. 7 as arising phase 704, a peak phase 705, a falling phase 706, an undershootphase 714, and finally a refractory period 717. During rising phase 704,the membrane voltage continues to depolarize. The point at whichdepolarization ceases is shown as peak phase 705. In the illustrativeembodiment of FIG. 7, at this peak phase 705, the membrane voltagereaches a maximum value of approximately 40 mV.

Following peak phase 705, the action potential underfoes falling phase706. During falling phase 706, the membrane voltage becomes increasinglymore negative, sometimes referred to as hyperpolarization of the nervecell. This hyperpolarization causes the membrane voltage to temporarilybecome more negatively charged then when the nerve cell is at rest. Thisphase is referred to as the undershoot phase 714 of action potential702. Following this undershoot, there is a time period during which itis impossible or difficult for the nerve cells to fire. This time periodis referred to as refractory period 717.

Action potential 702 illustrated in FIG. 7 may travel along, for examplethe auditory nerve, without diminishing or fading out because the actionpotential is regenerated each nerve cell. This regeneration occursbecause an action potential at one nerve cell raises the voltage atadjacent nerve cells. This induced rise in voltage depolarizes adjacentnerve cells thereby provoking a new action potential therein.

As noted above, the nerve cell must obtain a membrane voltage above acritical threshold before the nerve cell may fire. Illustrated in FIG. 7are several failed initiations 716 which occur as a result of stimuliwhich were insufficient to raise the membrane voltage above the criticalthreshold value to result in an action potential.

In normal hearing there is a level of spontaneous or random nerveactivity in the absence of sound that is inaudible to an individual.This spontaneous nerve activity is the result of the random release ofneurotransmitters by the cochlea hair cells. When a neurotransmitter israndomly released (in the absence of sound), the neurotransmitter causesthe spontaneous firing of an auditory nerve cell. Many of these combineto cause a level of inherent background noise. However, in cochlearimplant recipients and other individuals, such as individuals sufferingfrom tinnitus, this spontaneous nerve activity is lacking

One aspect of the present invention is directed to invoking stochasticor random activity within a nerve cell, referred to as pseudospontaneousnerve activity, through the application of one or more opticalstimulation signals to the nerve cells. In certain embodiments, thispseudospontaneous nerve activity replicates the spontaneous or randomnerve activity experienced by individuals with normal hearing. Byreplicating the naturally occurring spontaneous activity cochlearimplants may provide stimulated hearing that more closely replicatesnatural hearing. This may advantageously facilitate more accurate speechperceptions and/or the suppression of tinnitus. In certain embodimentsof the present invention, the intensity of the optical stimulationsignals which encourage, facilitate or allow the pseudospontaneous nerveactivity is below the recipient's perception or auditory threshold.

FIG. 8 is two graphs showing nerve activity for a given membranevoltage. Graph 801 illustrates membrane voltage of a nerve cell priorto, and during the application of an optical stimulation signalconfigured to encourage, facilitate or allow pseudospontaneous nerveactivity. Graph 803 illustrates the corresponding random nerve firingcaused by internal metabolic activity.

Referring to graph 801, the resting potential 802 of a nerve cell isapproximately −70 mV. At a first time, an optical stimulation signal isapplied to the recipient's cochlea to depolarize the nerve cells. Theoptical stimulation signal has an intensity which depolarizes the nervecells to slightly below the critical threshold 807 which, in theembodiment of FIG. 8, is approximately −50 mV. As noted above, once themembrane voltage increases to this level, the nerve cells may firerandomly as a result of the internal metabolic nerve activity within thenerve cells.

Graph 803 includes a number of spikes 805 illustrating thepseudospontaneous nerve activity which occurs while the nerve cells havea membrane voltage above the critical threshold. Each spike indicates afiring of a nerve cell. As shown, these firings occur at random or atleast semi-random times following application of the optical stimulationsignal.

Electrical stimulation signals generally include a positive pulsefollowed by a negative pulse. The positive pulse depolarizes the nervecells, while the negative pulse hyperpolarizes the nerve cells, therebyproviding charge recovery and eliminating the depolarization. Thischarge recovery prevents generation of toxic electrochemical by-productsin the cochlea as well as prevents damage to an electrical contact whichwould be caused by multiple pulses having the same polarity.

In contrast, electromagnetic (EM) radiation does not generate toxicby-products within the cochlea. As such, charge recovery utilized inelectrical stimulation is not required. As such, an optical stimulationsignal may comprise a pulse of EM radiation of any time duration.

FIG. 9 is two graphs illustrating exemplary optical and electricalstimulation signals that may be applied to a recipient's nerve cells. Anoptical stimulation signal 902, shown in graph 901, is applied at anintensity 931 which depolarizes the nerve cells to less than or up tothe critical threshold. As shown, optical stimulation signal 902comprises a pulse of electromagnetic (EM) radiation which is applied ata first time. The EM radiation is continuously applied for some periodof time. Because the nerve cells are depolarized to or near the criticalthreshold, pseudospontaneous nerve activity occurs in the nerve cells.

Graph 903 illustrates electrical stimulation signals 904. Stimulationsignals 904 represent one or more frequency components of a sound signaland are delivered to a recipient's cochlea 140 (FIG. 1) at an intensity933 to evoke a hearing percept by the recipient of the one or morefrequency components. In the illustrative embodiment of FIG. 9,electrical stimulation signals 904 are applied concurrently with opticalstimulation signal 902 to different nerve populations.

As noted above, in normal hearing, spontaneous nerve activity occurs inthe absence of sound. However, such spontaneous nerve activity alsooccurs prior to, during or subsequent to perception of a sound in normalhearing. This spontaneous nerve activity enhances the sound perceptionby more closely replicating natural hearing. Because electricalstimulation signals 904 are delivered concurrently with opticalstimulation signal 902 to encourage, facilitate or allow internalmetabolic activity to cause pseudospontaneous nerve activity, therecipient may experience a hearing percept which is superior to thatprovided by conventional cochlear implants.

As noted, the embodiments illustrated in FIG. 9 are merely illustrativeand should not be considered to limit the scope of the presentinvention. For example, in alternative embodiments, electricalstimulation signals 904 may be applied prior to, or subsequent toapplication of optical stimulation signals 902.

As would be appreciated by one of ordinary skill in the art, optical andelectrical stimulation signals may be delivered to the same or differentpopulations. In the illustrative embodiments of FIG. 9, the signals aredelivered to different nerve cell populations which, as described above,enhances the sound perception. In alternative embodiments in which theoptical and electrical signals are delivered to the same nerve cellpopulations, the optical and electrical signals may be delivered atdifferent times to avoid overstimulation of the nerve cells.

FIG. 10A is a high level flowchart illustrating operations that may beperformed to stimulate the nerve cells of a recipient in accordance withembodiments of the present invention. The stimulation process begins atblock 1002. At block 1004, one or more optical stimulation signals areapplied to the recipient's nerve cells at a duration and intensity toencourage, facilitate or allow pseudospontaneous nerve activity. Thestimulation process then ends at block 1008.

FIG. 10B is a detailed flowchart illustrating the operations that may beperformed in accordance with embodiments of block 1004 of FIG. 10A. Theoperations begin at block 1010. At block 1012, a decision is made if asound signal has been received and/or whether the signal should beprocessed. If a received sound signal is to be processed, the methodprogresses to blocks 1014 and 1015. At block 1015, one or more opticalstimulation signals are generated and applied to the recipient's nervecells at an intensity and duration that to encourage, facilitate orallow pseudospontaneous nerve activity. At block 1014, electricalstimulation signals based on the received sound signal are generated andapplied to the recipient's nerve cells. The operations of blocks 1015and 1014 may occur sequentially or concurrently. The operations then endat block 1022.

Returning to block 1012, if no sound signal is to be processed, themethod progresses to block 1018. A block 1018 a determination is made asto whether pseudospontaneous auditory nerve activity is desired. Ifpseudospontaneous auditory nerve activity is not desired, the methodends at block 1022. However, if pseudospontaneous auditory nerveactivity is desired, the method continues to block 1020. At block 1020,one or more optical stimulation signals are generated and applied to therecipient's nerve cells at an intensity and duration to encourage,facilitate or allow pseudospontaneous auditory nerve activity. Themethod then ends at block 1022.

It would be appreciated that the embodiments illustrated in FIGS. 10Aand 10B are merely illustrative and should not be considered to limitthe scope of the present invention.

As noted above, described aspects of the present invention are generallydirected to optically stimulating a recipient's nerve cells toencourage, facilitate or allow pseudospontaneous nerve activity. Otheraspects of the present invention are generally directed to deliveringcombinations of optical and electrical stimulation signals to arecipient's nerve cells to increase neural survival. For example,cochlear nerve cells which are not used to receive a hearing perceptwill eventually become non-functional. In other words, used spiralganglion or other cells will die and thus loss the ability to transmitelectrical potentials. Certain aspects of the present invention aredirected to increasing the neural survival rate of such unused cochlearnerve cells in a cochlear implant recipient. In these aspects, the nervecells are stimulated to evoke a hearing percept, and nerve cells whichare not used to perceive a sound are sequentially or concurrentlystimulated to maintain substantial neural survival of those cells. Theseaspects of the present invention may use the same cochlear implant asshown above in FIGS. 1, 3 and 4.

FIG. 11A illustrates optical and electrical stimulation signals 1102,1103 that may be applied to a recipient's cochlea 140 (FIG. 1). In graph1101, optical stimulation signals 1102 are generated based on a receivedsound signal. Optical stimulation signals 1102 are applied to cochlea140 at an intensity 1131 that exceeds the recipient's auditorythreshold, thereby evoking a hearing percept. As would also beappreciated, the duration, frequency and intensity of the opticalstimulation signals may depend on the received sound, the soundprocessing strategy used, the needs of the recipient, etc.

As shown in graph 1103, electrical stimulation signals 1104 are appliedto cochlea 140 following application of optical stimulation signals1102. Electrical stimulation signals 1104 are generated and applied tocochlea 140 at an intensity 1133 to maintain substantial neural survivalof the nerve cells. Intensity 1133 is preferably below the recipient'sauditory threshold. As would be appreciated, the intensity and/orfrequency of the electrical stimulation signals may depend on the needsof the recipient.

FIG. 11B illustrates optical and electrical stimulation signals 1106,1108, that may be applied to cochlea 140. In graph 1105, opticalstimulation signals 1006 are generated based on a received sound signal.Optical stimulation signals 1106 are applied at an intensity 1135 thatevokes a hearing percept by the recipient. In graph 1107, electricalstimulation signals 1108 are applied at an intensity 1137 to maintainneural survival. As shown, a first set 1110 of electrical stimulationsignals 1108 is delivered concurrently with optical stimulation signals1106 while a second set 1112 of electrical stimulation signals 1108 isapplied following application of optical stimulation signals 1106.

As would be appreciated by one of ordinary skill in the art, FIGS. 11Aand 11B illustrated specific examples of the embodiments describedabove. In certain embodiments, there is a likelihood that there is anoverlap of the optical and electrical stimulation signals on the samenerve cell population. In such embodiments, the intensities of thesignals would be moderated to prevent overstimulation of the nerve cellpopulation. This may be implemented, for example, by a time delay orreducing the signal intensity of one or more signals.

FIG. 12 is a flowchart illustrating a method 1201 performed duringoperation of cochlear implant 100. Method 1201 may be performedcontinually or periodically during operation. Illustrative method 1201begins at block 1216. At block 1218 a decision is made as to whether asound signal has been received and is to be processed. If the receivedsound signal is to be processed, the method progresses to block 1222.

At block 1222, a decision is made as to whether neural-survivalstimulation is also desired based on, for example, a user input, apre-programmed process, etc. If neural survival stimulation is notdesired, optical stimulation signals are generated based on the receivedsound signal and are applied to cochlea 140 (FIG. 1) at block 1226.However, if neural survival stimulation is desired, the method continuesto block 1223. That is, if cochlear implant 100 determines thatstimulation signals to evoke a hearing percept of the received soundsignal, and neural survival stimulation signals should be applied tocochlea 140, the method progresses to block 1223. At block 1223, opticalstimulation signals are generated based on the received sound signal,and are applied to the recipient's cochlea. Also at block 1223,electrical stimulation signals configured to maintain neural survivalare generated and applied to the recipient's cochlea. The method thenends at block 1234.

Returning to block 1218, if a received sound signal is not to beprocessed, the method progresses to block 1228. That is, if cochlearimplant 100 determines that no sound signal has been received, or atthat a received sound signal is not to be processed, the methodprogresses to block 1228. At block 1228, a decision is made as towhether neural-survival stimulation is desired. If neural survivalstimulation is not desired, the method ends at block 1234. However, ifneural survival stimulation is desired, the method continues to block1230. At block 1230, electrical stimulation signals configured tomaintain neural survival are generated and applied to the recipient'scochlea. The method then ends at block 1234.

As noted above, FIGS. 11A-12 illustrate embodiments of the presentinvention in which optical stimulation signals are used to evoke ahearing perception, and in which electrical stimulation signals are usedto maintain substantial neural survival. FIGS. 13A-14 illustratealternative embodiments of the present invention in which electricalstimulation signals are used to evoke a hearing percept and opticalstimulation signals are used to maintain neural survival.

FIG. 13A illustrates optical and electrical stimulation signals that maybe applied to a recipient's cochlea 140 (FIG. 1) in accordance withembodiments of the present invention. In graph 1303, electricalstimulation signals 1304 are generated based on a received sound signaland applied to cochlea 140 at an intensity 1331 to evoke a hearingpercept. As would be appreciated, the duration, frequency and intensityof the electrical stimulation signals may depend on the received sound,the sound processing strategy used, the needs of the recipient, etc. Ingraph 1303, following application of electrical stimulation signals1304, optical stimulation signals 1302 are applied to cochlea 140 at anintensity 133 to maintain neural survival. These neural-survivalstimulation signals have an intensity which is below the auditorythreshold of the recipient. As would be appreciated, the intensityand/or frequency of the optical stimulation signals may depend on theneeds of the recipient.

FIG. 13B illustrates other optical and electrical stimulation signalsthat may be applied to cochlea 140 in accordance with embodiments of thepresent invention. In graph 1305, optical stimulation signals 1108 aregenerated and applied to cochlea 140 to maintain neural survival. Ingraph 1307, electrical stimulation signals 1308 are generated andapplied to cochlea 140 based on a received sound signal to evoke ahearing percept. As shown, optical stimulation signals 1306 aredelivered concurrently with electrical stimulation signals 1308.

FIG. 13C still another exemplary optical and electrical stimulationsignals that may be applied to cochlea 140. In graph 1311, electricalstimulation signals 1312 are generated and applied to the recipient'scochlea based on a received sound signal to evoke a hearing percept. Ingraph 1305, an optical stimulation signal 1310 is concurrently generatedand applied to the recipient's cochlea to maintain neural survival.

FIG. 14 is a flowchart illustrating a method 1401 performed duringoperation of cochlear implant 100. Method 1401 may be performedcontinually or periodically during operation. Illustrative method 1401begins at block 1416. At block 1418 a decision is made as to whether asound signal has been received and is to be processed. If the receivedsound signal is to be processed, the method progresses to block 1422.

At block 1422, a decision is made as to whether neural-survivalstimulation is also desired based on, for example, a user input, apre-programmed process, etc. If neural survival stimulation is notdesired, electrical stimulation signals are generated based on thereceived sound signal and are applied to cochlea 140 (FIG. 1) at block1426. However, if neural survival stimulation is desired, the methodcontinues to block 1423. That is, if cochlear implant 100 determinesthat stimulation signals to evoke a hearing percept of the receivedsound signal, and neural survival stimulation signals should be appliedto cochlea 140, the method progresses to block 1423. At block 1423,electrical stimulation signals are generated based on the received soundsignal, and are applied to the recipient's cochlea. Also at block 1423,optical stimulation signals configured to maintain neural survival aregenerated and applied to cochlea 140. The method then ends at block1434.

Returning to block 1418, if a received sound signal is not to beprocessed, the method progresses to block 1428. That is, if cochlearimplant 100 determines that no sound signal has been received, or atthat a received sound signal is not to be processed, the methodprogresses to block 1428. At block 1428, a decision is made as towhether neural-survival stimulation is desired. If neural survivalstimulation is not desired, the method ends at block 1434. However, ifneural survival stimulation is desired, the method continues to block1430. At block 1430, electrical stimulation signals configured tomaintain neural survival are generated and applied to the recipient'scochlea. The method then ends at block 1434.

It would be appreciated that the above described embodiments are merelyprovided for illustration purposes, and the neural-survival stimulationparameters such as frequency, timing, location, etc. may vary. Forexample, the various characteristics of the neural-survival stimulationsignals may be controlled by, for example, a control module, such as thecontrol module described above with reference to FIG. 4. In someembodiments, the control module may cause the cochlear implant togenerate the electrical stimulation signals only when opticalstimulation signals have not been delivered for a period of time. Instill other embodiments, the electrical stimulation signals may begenerated when the cochlear implant enters a predetermined mode ofoperation, or device state, such as, for example, a sleep mode ofoperation.

In the aspects of the present invention described with reference toFIGS. 11A-14, stimulation signals configured to evoke a hearing perceptare generated and applied to a recipient's cochlea 140 (FIG. 1) incombination with stimulation signals configured to maintain substantialneural survival. In other aspects of the present invention, opticalstimulation signals are concurrently delivered to a region of therecipient's cochlea in order to reduce the intensity of electricalstimulation required to evoke a hearing percept during stimulatedhearing. These aspects of the present invention may use the samecochlear implant as shown above in FIGS. 1, 3 and 4.

In conventional electrically-stimulating cochlear implants, electricalstimulation signals must have a minimum intensity in order to evoke ahearing percept. Specifically, the electrical stimulation signals musthave an intensity which increases the membrane voltage of the cells fromthe resting level (resting potential) to a level at which the nervecells will fire. The minimum required intensity is referred to herein asa recipient's auditory threshold level. Embodiments of the presentinvention reduce this required intensity by applying an opticalstimulation signal to the recipient's auditory nerve cells prior to andduring application of electrical stimulation signals. The opticalstimulation signal has an intensity which increases the membrane voltageof the nerve cells to less than or equal to approximately therecipient's critical threshold. As described above with reference toFIG. 7, nerve cells having a membrane voltage at or near the recipient'scritical threshold will fire more readily than cells having a membranevoltage at the resting potential. Therefore, because the nerve cellswill fire more readily, electrical stimulation signals having anintensity below the recipient's auditory threshold level will cause theoptically stimulated nerve cells to fire, thereby evoking a hearingpercept.

FIG. 15 is two graphs illustrating an optical stimulation signal 1504delivered to a recipient's cochlea 140, and the resulting increase inmembrane voltage. As shown, optical stimulation signal 1504 has anintensity 1509 which is below the recipient's auditory threshold level.This intensity is referred to as sub-auditory intensity 1509. As notedabove, application of optical stimulation signal 1504 increase themembrane potential of the stimulated nerve cells to approximately therecipient's critical threshold 1507.

FIG. 16 is two graphs illustrating optical and electrical stimulationsignals that may be generated and applied to a recipient's cochlea 140.Graph 1601 illustrates an optical stimulation 1602 which increases themembrane voltage of nerve cells of cochlea 140 to approximately lessthan or equal to the recipient's critical threshold. Graph 1603illustrates electrical stimulation signals 1604 which, in combinationwith optical stimulation signal 1602, evoke a hearing response. Asshown, both optical stimulation signal 1602 and electrical stimulationsignals 1604 have sub-auditory threshold intensities 1607, 1609. In theembodiments of FIG. 16, electrical stimulation signals 1604 aregenerated and applied to the optically stimulated nerve cells afteroptical stimulation signal 1602 increases the membrane voltage of thenerve cells to the critical threshold.

FIG. 17 is a flowchart illustrating a method performed during operationof cochlear implant 100 in accordance with embodiments of FIG. 16. Themethod begins at block 1702. At block 1703, a sound signal is receivedby the cochlear implant. At block 1704, a sub-auditory threshold opticalstimulation signal is generated and applied to a recipient's cochlea 140(FIG. 1). At block 1705, sub-auditory threshold electrical stimulationsignals are generated based on the received sound signal, and areapplied to cochlea 140. The method then ends at block 1708. As would beappreciated by one of ordinary skill in the art, the operations ofblocks 1705 and 1704 occur concurrently, with appropriate delays forgeneration and/or application of electrical stimulation signals so thatthe membrane voltage of the nerve cells increases to the criticalthreshold.

The aspects of the present invention described above with reference toFIGS. 15-17 have been described with reference to delivery of an opticalstimulation signal comprising a single pulse of electromagnetic (EM)radiation. It would be appreciated that in other embodiments multiplepulses of EM radiation may be used to increase the membrane voltage ofnerve cells of cochlea 140. In these embodiments, optical stimulationsignals would be generated and applied to cochlea 140 at a frequencywhich causes the membrane voltage to remain at or near or lower than therecipient's critical threshold.

Likewise, the embodiments of FIGS. 15-17 have been described withoptical stimulation signals which increase the membrane voltage of thenerve cells of cochlea 140 to approximately the recipient's criticalthreshold. It would be appreciated that in other embodiments, theoptical stimulation signals may have an intensity which increases themembrane voltage to levels other than at or close to the criticalthreshold.

Several aspects of the present invention have been described withreference to the cochlear implant illustrated in FIGS. 1, 3 and 4. Inbrief review, such a cochlear implant terminates in a stimulatingassembly which comprises a longitudinally aligned and distally extendingarray of stimulating contacts disposed along a length thereof. In mostapplications of the present invention, the contact array comprisesoptical and electrical contacts via which stimulation signals areapplied.

FIGS. 18A-18E illustrate embodiments of a stimulating assembly 1818having different arrangements of optical contacts 1820 and electricalcontacts 1830. For ease of illustration, electrical contacts 1830 aredepicted as rectangles and optical contacts 1820 are depicted as ovals.These exemplary shapes are provided only to facilitate understanding ofembodiments of the present invention and do not define or limitelectrical contacts 1830 or optical contacts 1820 in any manner.

In FIG. 18A, a distal portion 1816A of a stimulating assembly 1818A isillustrated. As shown, electrical contacts 1830 and optical contacts1820 are arranged in an alternating fashion. In other words, in theillustrated arrangement of FIG. 18A, no optical contacts 1820 areadjacent other optical contacts. Similarly, no electrical contacts 1830are adjacent other electrical contacts. In contrast, as shown in FIG.18B, a smaller number of optical contacts 1820 are dispersed alongdistal portion 1816B within a contact array which is primarily comprisedof electrical contacts 1830. In the embodiment illustrated in FIG. 18C,a single optical contact 1820 is shown. Optical contact 1820 ispositioned at the proximal end of distal portion 1816C.

In FIG. 18D, two optical contacts 1820 are shown. Optical contacts 1820are positioned at the distal end 1832 of distal portion 1816D. Thisarrangement illustrated in FIG. 18D may be useful, for example, in theembodiments described in greater detail below with reference to FIGS.19-21. In the embodiment illustrated in FIG. 18E, distal portion 1816Eincludes only optical contacts 1820. Stimulating assembly 1818E may beused in embodiments of the present invention in which electricalstimulation is unnecessary or undesired.

As would be appreciated, the embodiments of FIGS. 18A-18E are providedfor illustrative purposes only, and any arrangement or combination ofoptical and/or electrical contacts 1820, 1830 may be used in the variousaspects of the present invention. The number of contacts may depend on,for example, the desired application, the needs of the recipient, etc.

The above aspects of the present invention have been described hereinwithout reference to the position of the stimulating assembly within arecipient's cochlea. However, because, as noted above with reference toFIGS. 2A and 2B, the cochlea is tonotopically organized, position and/orgeometry of the stimulating assembly, or of particular contacts, mayimpact the recipient's response to stimulation signals. For example, incertain aspects of the present invention, a stimulating assembly mayextend through the basal region of the recipient's cochlea towards theapical end of the cochlea. In these embodiments, the stimulatingassembly is inserted at least to the first turn of the cochlea, andsometimes further. In alternative aspects of the present invention, astimulating assembly, referred to as a short stimulating assembly, isimplanted only in the basal region of the cochlea. Such alternativeaspects of the present invention are described below with reference toFIGS. 19 and 20.

A short stimulating assembly is advantageously used to treat the portionof the hearing impaired population who suffer from sensorineual hearingloss only in the basal region of the cochlea. Due to the tonotopicorganization of the cochlea, such individuals maintain the ability toperceive middle to lower frequency sounds naturally, but have limited orno ability to perceive high frequency sounds. For such individuals,cochlear implants which may be implanted without damage to the residualhearing of a recipient, but which are configured to stimulate regions ofthe cochlea which are sensitive to high frequencies are beneficial.

One such short stimulating assembly is shown in FIG. 19. Shortstimulating assembly 1918 is configured to be fully implanted only inthe basal region 1932 of a recipient's cochlea 140. For ease ofillustration, a simplified view of cochlea 140 is shown. As such, thescala tympani and the scala vestibule have not been differentiated inFIG. 19. It would be appreciated that short stimulating assembly 1918may be inserted into either the scala tympani or the scala vestibuli ofcochlea 140.

When short stimulating assembly 1918 is fully implanted, distal end 1936of the stimulating assembly is positioned at or near distal end 1939 ofbasal region 1932. Alternatively, when short stimulating assembly 1918is fully implanted, distal end 1936 of the stimulating assembly ispositioned within basal region 1932. As used herein, the basal region1932 of cochlea 140 is the portions of the scala tympani and the scalavestibuli extending from the round window and oval window, respectively,to the first turn 1941 of cochlea 140. Therefore, when short stimulatingassembly 1918 is fully implanted in only the basal region of cochlear140, distal end 1936 of the short stimulating assembly is positioned at,in, or proximate to the region of cochlea 140 at which the first turn1941 of cochlea 140 begins. As used herein, the positioning of distalend 1936 in this region of cochlea 140 includes positions of distal end1936 in basal region 1932 or in first turn 1941.

Short stimulating assembly 1918 includes one or more optical contacts1920 to apply optical stimulation signals 1922 to cochlea 140. In theembodiments of FIG. 19, short stimulating assembly 1918 has threeoptical contacts 1920 positioned at distal portion 1916. Distal portion1916 is configured so that optical contacts 1920 are able to applyoptical stimulation signals 1922 to the portions of the scala tympaniand the scala vestibuli positioned proximate to cochlear apex 1924(referred to as apical region 1945) and the portions of the scalatympani and the scala vestibuli positioned between basal region 1932 andapical region 1945 (referred to as medial region 1943).

Specifically, when short stimulating assembly 1918 is fully implanted,at least one optical contact 1920 is positioned opposite of modiolarwall 1947 of first turn 1941 such that there is a direct line of sightpath between the optical contact 1920 and modiolar wall 1947. Due to thedirect line of sight path, optical stimulation signals 1922 aredelivered by the optical contact 1920 to modiolar wall 1947. In specificembodiments, the distal portion 1916 of short stimulating assembly 1918is angled towards modiolar wall 1947 during or after insertion of theshort stimulating assembly. The angling of distal portion 1916 improvesthe line of sight path between optical contacts 1920 and modiolar wall1947.

As shown in FIG. 19, short stimulating assembly 1918 also includes aplurality of electrical contacts 1930. Electrical contacts 1930 areconfigured to apply electrical stimulation signals (not shown) to basalregion 1932 of cochlea 140. It would be appreciated that the embodimentsillustrated in FIG. 19 are merely illustrative and other arrangements ofoptical contacts 1920 and electrical contacts 1930 may be used. Forexample, in alternative embodiments, one or more optical contacts 1920may be disposed along short stimulating assembly 1918 in basal region1932. In other embodiments, short stimulating assembly 1918 may comprisea single optical contact 1920 positioned at distal end 1936. In stillother embodiments, short stimulating assembly 1918 may include noelectrical contacts.

In the exemplary embodiment of FIG. 19, electrical stimulation signalsare applied to basal region 1932 to evoke a hearing percept of highfrequency components of a sound signal. Similarly, optical stimulationsignals 1922 are delivered to medial region 1943 of cochlea 140 to evokeperception of middle to low frequency components of a sound signal.These illustrative embodiments may be particularly beneficial forpatients with progressing hearing loss. As noted above, a shortstimulating assembly having only electrical contacts thereon (generallyreferred to as an electrode assembly) is generally implanted in arecipient who suffers only high frequency hearing loss. A shortelectrode assembly is used over a longer electrode assembly so that themedial and apical regions of the cochlea that naturally perceive middleand low frequency sounds remain intact. However, over time certainindividuals lose the ability to naturally perceive middle and lowfrequency sounds. In such individuals who previously received a shortelectrode assembly, the electrode assembly must be removed from thecochlea and replaced with a longer electrode assembly that canelectrically stimulate the middle or low frequency regions of thecochlea. Short stimulating assembly 1918 may reduce the need for suchfuture surgery. Specifically, short stimulating assembly 1918 may beimplanted in basal region 1932 in a minimally invasive manner withoutdamaging the medial 1943 and apical 1945 regions of cochlea 140.Stimulating assembly 1918 would be configured to stimulate (opticallyand/or electrically) high frequency responsive basal region 1932. If ata later time the recipient losses the ability to perceive middle and/orlow frequencies, optical contacts 1920 may be used to opticallystimulate medial 1943 and/or apical 1945 regions of cochlea 140.Providing such optical stimulation to medial 1943 and/or apical 1945regions of cochlea 140 does not require an additional surgicalprocedure, but rather requires a reprogramming of the cochlear implant.

It should be appreciated that in certain embodiments of the presentinvention, it is not necessary to obtain a direct line of sight pathbetween optical contacts 1920 and medial 1943 and/or apical 1945 regionsof cochlea 140 in order to evoke perception of middle or lowfrequencies. As would be appreciated, nerves corresponding to the lowand middle frequencies pass behind modiolar wall 1947 of basal turn1941. As such, in embodiments of the present invention, the spatiallyselectivity provided by optical stimulation signals may be used tostimulate the middle and/or low frequency nerves passing behind modiolarwall 1947.

As described above, aspects of the present invention generate and applyoptical and/or electrical stimulation signals to cochlea 140 to providea variety of therapeutic benefits. For example, optical stimulationsignals may be applied to generate pseudospontneous nerve activity, toevoke a hearing percept, to maintain neural survival, etc. Electricalstimulation signals may be applied to evoke a hearing percept, maintainneural survival, etc. Furthermore, combinations of optical andelectrical stimulation signals may be applied to collectively evoke ahearing percept. It should be appreciated that short stimulatingassembly 1918 may be used in any of the above or other aspects of thepresent invention.

FIG. 20 is a top-view of a distal region 2016 of a short stimulatingassembly 2018 in accordance with embodiments of the present invention.In the illustrated embodiment, distal region 2016 comprises multipleoptical contacts 2020, however in other embodiments a single contact maybe utilized. Each contact 2020 is configured to direct opticalstimulation signals to medial and or apical regions of cochlea 140 (FIG.1). As would be appreciated, the arrangement of optical contacts 2020shown in FIG. 20 is merely illustrative.

Aspects of the present invention have described herein with reference tothe cochlear implant illustrated in FIGS. 1, 3 and 4. Specifically, inreview, a cochlear implant 400 shown in FIG. 4 includes anelectromagnetic radiation (EMR) generator 462 which generates opticalstimulation signals 463. The optical stimulation signals 463 compriseelectromagnetic energy which is generated and delivered to cochlea 140.As noted above, the electromagnetic energy may have any wavelength, andis not limited to electromagnetic energy within the optical spectrum.For example, in specific embodiments of the present invention, EMRgenerator 463 is a light source. The wavelength of the light used inthese embodiments is not necessarily limited to the visible range ofapproximately 350 to 750 nanometers (nm), but rather may includeultraviolet, visible, infrared, far infrared or deep infrared light. Forexample, in certain embodiments, infrared light having wavelengthsbetween about 750 nm and 1500 nm may used. In other embodiments, lighthaving longer or shorter wavelengths may also be used.

In the embodiments described above with reference to FIG. 4, the lightsource would comprise part of a stimulator unit 402 that also includesan electrical stimulation signal generator 460. However, as noted above,other arrangements may be implemented in embodiments of the presentinvention. FIG. 21 illustrates such an alternative arrangement of aportion of a stimulating assembly 2118.

In the embodiments of FIG. 21, two light sources, shown as micro-lasers2120 are integrated into carrier member 2114 of stimulating assembly2118. Micro-lasers 2120 generate optical stimulation signals in the formof light 2132 which may be delivered to a cochlea (not shown).Micro-lasers 2120 may controlled by control signals received via signallines 2134.

As shown in FIG. 21, the light emitting portion of micro-laser 2620A ispositioned adjacent a rough surface 2112 of stimulating assembly 2118.Rough surface 2118 functions as an optical contact which disperses light2132A. In contrast, the light emitting portion of micro-laser 2120B ispositioned adjacent a converging lens 2110 integrated in, or disposed onthe surface of carrier member 2114. Converging lens 2610 functions as anoptical contact which substantially focuses light 2132B.

Although FIG. 21 is illustrated with reference to micro-lasers 2620embedded in carrier member 2114, it should be appreciated that otherlight generating or emitting sources, such as Light Emitting Diodes(LEDs) may also be embedded in the carrier member in place of themicro-lasers.

FIG. 22 illustrates elements of an internal component 2200 of a cochleaimplant in accordance with embodiments of the present invention. Asshown, similar to the above embodiments, the EM generator 2284, shown aslight source 2284, is not integrated or embedded in carrier member 2286of stimulating assembly 2218. Rather, light source 2282 comprises partof a stimulator unit, illustrated as printed circuit board (PCB) 2282.Embedded in carrier member 2286 is an optical fiber 2280 which coupleslight source 2284 to an optical contact 2220 of stimulating assembly2218. In the embodiments of FIG. 22, light source 2284 generates opticalstimulation signals which are directed to optical contact 2220 byoptical fiber 2280. FIG. 23 illustrates an exemplary optical fiber whichmay be used in embodiments of the present invention.

For ease of illustration, internal component 2200 is shown in FIG. 22 ascomprising one light source 2284, one optical fiber 2280, and oneoptical contact 2220. As described above, a stimulating assembly inaccordance with embodiments of the present invention may comprise aplurality of optical contacts 2220. As such, in embodiments of thepresent invention, carrier member 2286 may have a plurality of opticalfibers 2280 embedded therein to couple the optical contacts to lightsource 2284. Furthermore, in some such embodiments in internal component2200 may further include multiple light sources 2284 and multipleoptical fibers 2280.

As is well known in the art, an optical fiber is a type of waveguide.Waveguides include low bending loss fibers, photonic crystal fibers,telecom fibers, metal coated silica core fibers, etc. It should beappreciated that although FIG. 22 illustrates the use of one type ofoptical fiber 2280 to direct light to optical contact 2220, any othertype of waveguide could also be used in alternative embodiments.

In certain embodiments of the present invention, silicone carrier member2286 of stimulating assembly 2218 is used to guide optical stimulationsignals from an optical light source to the nerve cells of a recipient.In such an embodiment, the silicone acts as a mechanism to spread theoptical stimulation signals. In further embodiments, the carrier membersurface, or portions thereof, could be lined with a reflecting layer tominimize the loss or spread of light.

As noted above, FIG. 23 illustrates an exemplary optical fiber 2380 usedin embodiments of the present invention. FIG. 23 provides across-sectional view of a portion of optical fiber 2380. As is known inthe art, optical fiber 2380 carries light along its length. Opticalfibers may be made from glass (silica) or polymers such as polymershaving high refractive indices, such as Polyethersulfone (PES) andPolyphenylsulfone (PPS). As would be appreciated, any known waveguide oroptical-fiber structure may be used. As used herein, an optical-fiberstructure is an inclusive term that includes a single optical fiber aswell as a bundle of individual optical fibers, a fused bundle of opticalfibers, star couplers, and includes ferrules, lenses, and the like usedto couple light into and out of the optical fiber structure.

As shown, optical fiber 2380 comprises a core 2394 through which light2396 travels. Light 2396 is retained in core 2394 by total internalreflection caused by cladding 2392. In operation, light 2396 exits core2394 at one or more optical contacts (not shown). Exemplary opticalcontacts are described below with reference to FIGS. 27A and 27B.

In some embodiments, optical fiber 2380 is hermetically sealed.Materials which may be used to hermetically seal optical fiber 2380include, for example, parylene, diamond-like carbon, and platinum.

In certain embodiments, optical fiber 2380 may support many propagationpaths or transverse modes. Such fibers are referred to as multimodefibers (MMF). In contrast, fibers which support only a single mode arecalled single mode fibers (SMF). Embodiments of the present inventionmay use either a SMF or an MMF.

As is well known, light can be lost through the cladding of an opticalfiber at bends in the optical fiber. As such, the thickness of cladding2392 may vary depending on the light, application, acceptable losses,etc. Similarly, cladding 2392 may be doped to create an index ofrefraction which is useful in the desired application. In embodiments ofthe present invention, the optical fiber, or portions thereof, maycomprise a low bending loss fiber to prevent the loss of light. Theselow loss bending fibers may comprise, for example, photonic specialtyfibers. In still other embodiments of the present invention, thecladding of the optical fiber 2380 may be replaced with a reflectivecoating to reduce the size of the optical fiber. Such a coating couldoptionally function not only as a reflector for light, but also as aconductor for electrical stimulation signals.

In further embodiments of the present invention, the stimulatingassembly may comprise diffractive or refractive optics to steer light tospecific locations.

FIGS. 24A and 24B illustrate distal regions of two optical fibers 2480,2481 in accordance with embodiments of the present invention. Opticalfiber 2480 is shown in FIG. 24A. As shown, light 2432 is transmittedthrough core 2460 and retained therein core by total internal reflectioncaused by cladding 2462. As shown, optical fiber 2480A comprises astandard telecom fiber in combination with a micro-lens 2464 which actsas an optical contact which focuses light 2432.

Optical fiber 2481 is illustrated in FIG. 24B. Optical fiber 2481 issubstantially similar to optical fiber 2480 expect that optical fiber2481 includes a reflective element 2466. In this embodiment, as light2432 is transmitted through core 2460, the light impinges uponreflective element 2466 to reflect the light an angle of 90°. Reflectiveelement 2466 directs light to micro-lens 2464 which acts as an opticalcontact to focus light 2432. Reflective element 2466 may comprise amirror, a glass/polymer to air interface, or a reflective coatingdeposited on an interior surface of optical fiber 2481.

As discussed above, at least two approaches may be taken to opticallystimulate a recipient's nerve cells. In one embodiment explained abovewith reference to FIG. 21, a light source may be embedded in a carriermember adjacent an optical contact. In other embodiments described abovewith reference to FIGS. 22-24B, the light source may be located at adistance from an optical contact with a waveguide delivering the lightfrom the source to the optical contact. In either of these embodiments,various different types of light sources may be used. Specifically, anylight source that meets the shape, size, wavelength and/or intensitydemands of the specific embodiment may be used. Exemplary lights sourcesinclude, but are not limited to, light emitting diodes (LEDs), laserdiodes and lasers or microlasers (collectively lasers herein) such asVertical Cavity Surface Emitting Lasers (VCSELs), free electron lasers(FELs), etc.

FIG. 25 illustrates the structure of an exemplary VCSEL 2540 which maybe used in accordance with embodiments of the present invention. VCSEL2540 is a type of semiconductor laser diode having laser beam emissionperpendicular from a top surface of metal contact 2530. This is contraryto conventional edge-emitting semiconductor lasers which emit lightsfrom surfaces formed by cleaving the individual chip out of a wafer. Asshown, VCSEL 2540 consists of two distributed Bragg reflector (DBR)mirrors 2532, 2534 positioned parallel to a wafer surface or substrate2536. As shown, the upper and lower mirrors 2532 and 2534 are doped asp-type and n-type materials, respectively, forming a diode junction.

As noted above, several different waveguides may be used to guide lightto an optical contact. As is well known in the art, waveguides aresensitive to bending losses. In other words, when a waveguide is bent,light will pass through the cladding. FIG. 26 illustrates an embodimentof the present invention may be configured to take advantage of suchbending losses. Specifically, in the embodiment of FIG. 26, a portion ofthe light, shown by arrow 2670, passes through the cladding (not shown)of optical fiber 2636 and impinges onto a surface of stimulatingassembly 2618. In this embodiment, the interior or outer surface ofstimulating assembly 2618 has a reflective coating 2672. When theportion of light 2670 impinges on this reflective surface, the light isreflected back through the optical fiber towards electrical contacts2630 and impinges upon nerve cells of the recipient.

FIGS. 27A and 27B illustrate exemplary lenses which may be used asoptical contacts in accordance with embodiments of the presentinvention. Specifically, FIG. 27A is an enlarged view of a converginglens 2710 that may be used in an optical contact in accordance withembodiments of the present invention. Similarly, FIG. 27B is an enlargedview of a diverging lens 2712 that may be used in an optical contact inaccordance with embodiments of the present invention.

As would be appreciated, it may be possible to omit lens from thestimulating assembly by polishing the end of the waveguideappropriately. However, the use of a lens provides more design optionsand may provide an enhanced ability to direct optical stimulationsignals. The lens may be manufactured by molding the lens from silicone.The shape of a lens may be determined by considering the physicalproperty of the material used, and the interface property of thematerial to the perilymph (lens profile, change in refractive index atthe interface, surface roughness). In embodiments of the presentinvention, a spherical lens or aspeherical lens may be used.

In further embodiments of the present invention, the optical contactsmay be movable, slidable, re-shapeable, or otherwise adjustable to allowfor adjustment of the direction of the optical stimulation signals afterimplantation.

As would be appreciated, optical contacts may be negatively impacted bythe build up of fibrous tissue thereto. As such, in certain embodimentsof the present invention, the optical contacts are treated withanti-fibrotic treatments to protect the contacts from being impacted byfibrous tissue. These treatments could be delivered via surface geometryor via drugs.

As discussed above, conventional electrically stimulating devicesrequire initial and/or periodic fitting or programming procedures todetermine the current required to evoke a hearing percept. Thisgenerally requires determination of one or both of a recipient'sthreshold (T) level, and comfort (C). The fitting procedure may useeither subjective or objective feedback (neural response telemetry (NRT)measurements) to obtain the T and C levels.

As with electrical stimulation, the T and C levels may also need to beestablished for optically stimulating channels of a cochlear implant. Afitting procedure using subjective and/or objective feedback (NRTmeasurements) would be used to obtain the T and C levels.

In certain embodiments of the present invention, the time required forsuch a fitting procedure may be reduced by using several advantagesprovided by NRT. Specifically, in certain embodiments, the recipient'scochlea is stimulated via an electrical contact, and the response of thenerve cells is measured at recording contact. Following this, opticalstimulation would be provided via an optical contact and the resultingresponse would also be measured. The ratio of both T and C's for theelectrical contact and the optical contact could then be correlated.This information would be used to assist in finding the T and C valuesfor other optical and electrical contacts.

As noted above, a neural-stimulating device in accordance withembodiments of the present invention delivers optical and/or electricalstimulation signals to nerve cells of a recipient. In accordance withembodiments of the present invention, the stimulated nerve may be cellsof any nerve, such as motor or sensory nerves in the peripheral nervoussystem, nerve tissue of the central nervous system (nerves within thebrain and spinal cord), the cranial nerves (e.g., the optic nerve, theolfactory nerve, the auditory nerve, and the like), the autonomicnervous system, as well as brain tissue and/or any other neural tissue.Thus, the tissue to which optical and/or electrical stimulation signalsare applied need not itself be a “nerve” as conventionally defined, butcould include brain tissue that when stimulated by light or currentinitiates a response similar to that carried by a nerve, e.g., an actionpotential that includes electrical and/or chemical components, and whichis propagated to a location some distance from the point that wasoptically stimulated.

Further features and advantages of the present invention may be found incommonly owned and co-pending U.S. patent application entitled “ANEURAL-STIMULATING DEVICE FOR GENERATING PSEUDOSPONTANEOUS NEURALACTIVITY,” and commonly owned and co-pending U.S. patent applicationentitled “AN OPTICAL NEURAL STIMULATING DEVICE HAVING A SHORTSTIMULATING ASSEMBLY,” both filed concurrently herewith. Both of theseapplications are hereby incorporated by reference herein in theirentirety.

All documents, patents, journal articles and other materials cited inthe present application are hereby incorporated by reference.

Embodiments of the present invention have been described with referenceto several aspects of the present invention. It would be appreciatedthat embodiments described in the context of one aspect may be used inother aspects without departing from the scope of the present invention.

Although the present invention has been fully described in conjunctionwith several embodiments thereof with reference to the accompanyingdrawings, it is to be understood that various changes and modificationsmay be apparent to those skilled in the art. Such changes andmodifications are to be understood as included within the scope of thepresent invention as defined by the appended claims, unless they departthere from.

What is claimed is:
 1. A method for stimulating nerve cells of arecipient comprising: generating one or more optical stimulationsignals; delivering said one or more optical stimulation signals to thenerve cells; generating electrical stimulation signals; and deliveringsaid electrical stimulation signals to the nerve cells.
 2. The method ofclaim 1, wherein generating said one or more stimulation signalscomprises: generating said one or more optical stimulation signals witha light source, and wherein said one or more optical stimulation signalsgenerated by said light source are in the optical spectrum.
 3. Themethod of claim 1, wherein the nerve cells comprise spiral ganglioncells of the recipient, and wherein said method further comprises:delivering said one or more optical stimulation signals to the spiralganglion cells.
 4. The method of claim 1, wherein generating said one ormore optical stimulation signals comprises generating a plurality ofoptical stimulation signals; and independently delivering each of saidplurality of optical stimulation signals to the nerve cells.
 5. Themethod of claim 1, wherein generating said one or more opticalstimulation signals comprises generating a plurality of sets of opticalstimulation signals; and independently delivering each of said pluralityof sets of optical stimulation signals to the nerve cells.
 6. The methodof claim 1, wherein said delivering said one or more optical stimulationsignals to the nerve cells comprises: delivering said one or moreoptical stimulation signals via an optical contact configured todisperse said one or more optical stimulation signals.
 7. The method ofclaim 1, wherein said delivering said one or more optical stimulationsignals to the nerve cells comprises: delivering said one or moreoptical stimulation signals via an optical contact configured tosubstantially focus said one or more optical stimulation signals.
 8. Themethod of claim 1, further comprising: delivering said one or moreoptical stimulation signals and said electrical stimulation signals to asame region of the nerve cells.
 9. The method of claim 1, furthercomprising: receiving an acoustic sound signal; generating a set ofencoded signals based on said acoustic sound signal; generating said oneor more optical stimulation signals based on said set of encodedsignals; and delivering said one or more optical stimulation signals tothe nerve cells to cause perception by the recipient of one or morefrequency components of said acoustic sound signal, wherein deliver ofsaid electrical stimulation signals cause sub-threshold stimulation ofthe nerve cells.
 10. The method of claim 9, further comprising:concurrently delivering said electrical stimulation signals and said oneor more optical stimulation signals to the nerve cells.
 11. The methodof claim 9, further comprising: generating said electrical stimulationsignals which cause said sub-threshold electrical stimulation only whenan acoustic signal has not been received at said microphone for apre-determined period of time.
 12. The method of claim 9, furthercomprising: delivering said one or more electrical stimulation signalswhich cause said sub-threshold electrical stimulation at an intensity toattain substantial neural survival in the stimulated region of the nervecells.
 13. The method of claim 1, further comprising: receiving anacoustic sound signal; generating a set of encoded signals based on saidacoustic sound signal, generating said electrical stimulation signalsbased on said set of encoded signals; and delivering said electricalstimulation signals to the nerve cells to cause perception by therecipient of one or more frequency components of said acoustic soundsignal, wherein said one or optical stimulation signals causesub-threshold stimulation of the nerve cells.
 14. The method of claim13, further comprising: concurrently delivering said electricalstimulation signals and said one or more optical stimulation signals tothe nerve cells.
 15. The method of claim 13, further comprising:generating said one or more optical stimulation signals which cause saidsub-threshold optical stimulation only when an acoustic signal has notbeen received at said microphone for a pre-determined period of time.16. The method of claim 13, further comprising: delivering said one ormore optical stimulation signals which cause said sub-threshold opticalstimulation at an intensity to attain substantial neural survival in thestimulated region of the nerve cells.
 17. The method of claim 1, furthercomprising: generating one or more optical stimulation signalsconfigured to cause sub-threshold optical stimulation of the nervecells; generating electrical stimulation signals configured to causesub-threshold electrical stimulation of the nerve cells based on a setof sound processor-encoded signals; and concurrently delivering saidelectrical stimulation signals and said one or more optical stimulationsignals to the nerve cells, wherein said electrical stimulation signalsand said one or more optical stimulation signals collectively causeperception by the recipient of one or more frequency components of saidacoustic sound signal.
 18. The method of claim 17, wherein deliveringsaid one or more optical stimulation signals which cause saidsub-threshold optical stimulation comprises: delivering said one or moreoptical stimulation signals via an optical contact configured to causedispersed optical stimulation.
 19. The method of claim 17, whereindelivering said one or more optical stimulation signals which cause saidsub-threshold optical stimulation comprises: delivering said one or moreoptical stimulation signals via an optical contact configured to causesubstantially focused optical stimulation.